The invention relates to quality control in general, more particularly, to a system and method for automated process control of stages in articles manufacturing and most specifically to the integration of process control of separate manufacturing stages into a modular structure to yield a comprehensive automated process control of the complete production line. This invention is also related to U.S. patent application Ser. No. 09/633,824 by Goldman, et al. entitled xe2x80x9cStrategic Methods for Process Controlxe2x80x9d filed Aug. 7, 2000, to U.S. patent application Ser. No. 09/689,884 by Goldman, et al entitled xe2x80x9cSystem and Methods for Monitoring Process Quality Controlxe2x80x9d filed Oct. 13, 2000; and to U.S. patent application by Goldman, et al, entitled xe2x80x9cA method and Tool for Data Mining in Automatic Decision Making Systemsxe2x80x9d filed Dec. 8, 2000, all of which are incorporated by reference for all purposes as if fully set forth herein.
Process control plays a fundamental role in attaining high yield of quality products. Among various process control methods, statistical process control (SPC) is well known. SPC relies on the observation of the deviation of a measurable process output parameter in the process from their statistically predicted distribution (e.g. by more than three standard deviations). SPC reveals trends towards a deterioration of a process as well as temporarily irregularities of parameters of a process.
Prior attempts have been made to automate SPC.
U.S. Pat. No. 5,483,468 to Chen et al describes a system and method for concurrently recording and displaying system performance data by a computing system. In this invention a method is described in which a user interacts with the data being displayed to create various analysis of that data with the intentions of improving system performance.
U.S. Pat. No. 5,479,340 to Fox et al. describes a multivariate analysis of components of an ongoing semiconductor process for real time in-situ control. In this invention the algorithm calculates the T2 value from lotteling T2 statistical analysis which in turn creates a feedback signal if the T2 value is out of range and stops the process.
U.S. Pat. No. 5,440,478 to Fisher et al. describes a method and system for controlling a manufacturing process using statistical indicators of performance from the production process and specification data. The data is entered into a computer and displayed in tables and bar graphs to enable the production control manager to see unfavorable trends and processes out of control to allow adjustment of the manufacturing process before the process run is completed.
U.S. Pat. No. 5,862,054 to Li describes a system for real time statistical process control having the capability to monitor multiple process machines at the same time with a mix of different types of machines. The specific implementation of that invention is in connection with semiconductor wafer fabrication process machinery such as for ion replantation. It is also applicable to other processes and process equipment where it is necessary for automatic collection of process parameter data for SPC and the subsequent usage of the data to show trends and the goodness of the operating machinery.
All the aforementioned techniques suffer from inherent limitations resulting from the fact that their focus is the controlled variable, without linking the parameters, which influence the controlled variable. Thus, these techniques lack the ability to identify the combination of factors in a multi factorial process which is responsible for an observed deviation of an output of a process. Consequently, the process controlled by these methods can""t be rectified on the fly, but rather can only be halted until the process engineer finds out the related problem.
To overcome this drawback, Goldman, et al in their patent application Ser. No. 09/689,894 entitled: xe2x80x9cSystem and Method for Monitoring Process Quality Controlxe2x80x9d (hereinafter the POEM Application), described a method for an advanced process control (APC) which is essentially an on line monitoring and control of process parameters aimed to yield a robust process output having optimum statistical attributes (such as Cp and Ck).
A modern production line comprises a great number of process stages performed in series by a diversity of manufacturing tools, thus a work piece which consist of an output of a first manufacturing tool is delivered as an input entity to a second manufacturing tool and so on until the product is finally shaped.
Furthermore, the term xe2x80x9cmanufacturing toolxe2x80x9d represents a plurality of units performing the same process on various article in parallel, e.g. a line of polishing machines in a microelectronic facility, each polishing one wafer at its time in accordance with the peculiar conditions of the machine, or a tool which can handle a plurality of items at once e.g. a diffision oven which handle tenth of wafers in a single run.
Until now, no quality control method did try to cope with the challenge that due to the xe2x80x9cfact of lifexe2x80x9d that a production tool is not always tuned and therefore the designed nominal values of a process output carried out by this tool may vary within its tolerances in such a way that the final target will not be achieved. The present invention suggests a corrective action to be taken to xe2x80x9csavexe2x80x9d final target quality. This is achieved by a trade off mechanism which is based on a judicious combination of the deviating output with one or more other outputs which are deliberately diverted from their initially set target value.
Until now process control methods have been devised to control and optimize an output of a single stage in a multistage manufacturing process, and no attention was paid as to how the controlled parameters of a controlled first process affect an output of a subsequent second controlled process that follows (and functionally relies on the output of) the first stage. In addition, no attention was paid to the impact of subsequent stages output on previous stages outputs, with regard to the optimal values to be set as output targets.
As a result it is nowadays impossible to have a global process control, which integrally combines all the various steps in a processes.
The present invention fulfills this gap and provides other related advantages as is detailed below.
The present invention describes a method and system of a global process control, which integrally controls all the steps and stages in a process that lead a production item (e.g. a wafer in the semiconductor industry) through its voyage from raw material (a wafer) to the final product (a device).
The present invention leads to a totally different paradigm to run a production facility, where the intermediate targets for the individual machines are set dynamically during the process, in accordance with the final target for the finished product.
In accordance with the present invention there is provided a method for controlling a product quality during product manufacturing, the manufacturing includes a plurality of processes, each process among said plurality of processes has an assigned value of the process target output the method comprising the step of:
reassigning the value of the target output of a first process among said plurality of processes in accordance to an output of at least one second process.
In accordance with the present invention there is provided a method for controlling a product quality comprising the steps of: (a) assigning the product a predetermined criteria with respect to a performance of the product; (b) linking the performance to a feature of at least one structural element of the product and, (c) associating the feature of at least one structural element with at least one stage in a process which terms that at least one structural element, wherein at least two process stages are modular process controlled.
In accordance with the present invention there is provided a system for controlling a product quality in production, that includes a plurality of processes, each process among the plurality of processes has an assigned value of target output, wherein the assigned value of target output of a first process among the plurality of processes is reassigned during the occurrence of the production in accordance to an output value of a second process among the plurality of processes, the system comprising: (a) a mechanism for monitoring of the output value of the second process; (b) a mechanism for the evaluating the output value of the second process; (c) a mechanism for reassignment a value to target output of the first process according to the evaluation of the output value of the second process and; (d) a modeller to predict a feed forward input which results with the reassigned target value having best statistical goodness.